The Meta Conversions API (CAPI) lets you send conversions from your server, so Meta sees sales the browser pixel missed. Building it yourself means hashing data, matching click ids and deduplicating with the pixel.
BrainyMetrics sends Purchase and Lead events about 30 seconds after the conversion, with hashed email, phone, name and address, IP, user agent, fbc/fbp, value and contents. tracko.js observes your Meta pixel, so when it fired the same event its eventID is reused and Meta deduplicates. Leads that came from Meta Lead Ads aren't sent back, because Meta already counted them.